Gaming is what made Windows dominate personal computing - not Word, Excel or Powerpoint.
Gaming is what drives new hardware development, is what drives new personal computer ownership, and is what drives operating system preference.
For everyone else - a 10 year old computer does the job just fine... and it doesn't really matter what OS it happens to run.
Imagine if Apple had made it a point to dominate gaming too. Suddenly the folks spending $2-5K on a top of the line gaming machine would be forking it over for the latest generation of $5k Apple Desktops.